Vapor electric device



Aug. 20, 1935. L. R. LUDWIG El AL 2,011,543

,. I VAPOR ELECTRIC DEVICE Filed May 27, 1933 WITNESSES: INVENTORS. d gZeonfiludng an I jaseph 5/ep/an.

} ATTORNEY Patented Aug. 20, 1935 PATENT OFFICE VAPOR ELECTRIC DEVICELeon 8. Ludwig, Wllkinsburg, and Joseph Slepian, Pittsburgh, Pa.,assignors to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application May 27,

3 Claims.

Our invention relates to a vapor electricdevice and particularly to amercury arc rectifier or inverter. r

. In the development of mercury arc rectifiers, the greatest singleobstacle has been the tendency of the rectifiers to backfire at randomtimes under load. It has been discovered that the backfires arise fromcauses which are of relativelyshort duration with respect to the timeintrvals during which the rectifier is carrying current. If therectifier can be prevented from establishing an inverse current arc orbackfire during the period of prevalency of the backfire cause, nodamage will be done to the rectifier.

f Protective devices such as shields or grids have beemdeveloped forpreventing the formation of backfires; however, these protective deviceshave resulted in a material increase of the arc drop or losses in therectifier.

Rectifiersfor successful operation have, as heretofore constructed, hada plurality of anodes in a single large container and a plurality ofsafety devices such as grids, shields, series reactors, and otherdevices for preventing backfire. These large tanks and theirappurtenances have been very costly to construct and difilcult totransport and assemble.

Simple rectifiers comprising only a single anode and cathode closelyspaced in regard to each other may be constructed very cheaply.transported easily and assembled in almost any space having the desiredsize regardless of shape. However, the high backfire rate of such simpledevices has prevented their utilization.

'It is an object of our invention to provide a rectifier which isrelatively. free from backfires and in which it is unnecessary to usethe protective devices, such as grids or shields. Since backfire causesare of a random manner in time, it is highly improbable that tworectifiers will have a backfire cause simultaneously. Consequently,'iftwo simple rectifiers are connected in series, the probability of bothrectifiers having a simultaneous backfire cause is very remote. Also,if, for any reason, one of the rectifiers develops a backfire cause, theseries rectifier will prevent the inverse or backfire arc, and,accordingly, the backfire cause will vanish without doing any damage tothe rectifier.

The following comparison is given to illustrate the enormous gain inreliability by the device according to our invention. It was found thata simple rectifier as used in our invention has a backfire rate of oneper minute. Consequently, in a full-wave rectifier, an average of twoshort 1933, Serial No. 673,240

circuits per minute may be expected. However, when two such simplerectifiers are placed in series according to our invention, it isnecessary that both rectifiers fail simultaneously in order to cause ashort circuit. We have found that backfire causes usually last less thanseconds therefore the chance of backfire causes occurring simultaneouslyin each tube in one minute is Hence the two tubes in series will failsimultaneously and cause a short circuit on the average of only one in60x10 minutes or once in 11.4 years, the probability of failure in afull-wave rectifier being, therefore, once in 5.7 years.

It is a further object of our invention to provide a simple rectifierhaving means to regulate the formation of the rectifying are so that theoutput voltage or current of the rectifier can be controlled.

Other objects and advantages of our invention will be apparent from thefollowing detailed description taken in conjunction with theaccompanying drawing, in which:

Figure l is a schematic illustration of a simple rectifier according toour invention;

Fig. 2 is a modification showing control grids;

Fig. 3 is a further modification; and

Fig. 4 is an illustration of a'conventional rectifier modified accordingto our invention.

Apparatus according to our invention comprises a plurality of dischargechambers directly connected in series. Preferably these dischargechambers are of a simple nature, such as a plurality of conductingplates 3, separated by an insulating ring 4 forming a closed chamber 5.Suitable vaporizing material, such as mercury 6. is placed on thelowermost plate of each chamber 5. Preferably, the two chambers arebuilt as a unit with the bottom plate of the top chamber forming the topplate or anode of the bottom chamber. However, two separate devices maybe used. In any event, it is desirable to solidly and directly connectthe cathode of one chamber to the anode oi the succeeding chamber.

Any suitable means, such as a keep-alive Ill or a make-alive electrodeH, such as disclosed in our copending application Serial No. 620,866,may be used for initiating or maintaining a cathode spot on thevaporizable electrode 6. In some instances, it will probably be foundpreferable to use a combination of make-alive or keepalive electrodes inthe series-connected rectifying devices.

Our experiments have shown that it is desirable to provide means forequalizing the backvcltage over the series-connected rectifiers. Forpurpose, we prefer to use a high resistance 2-8 connected in parallelwith each of the seriesconnected devices but may use an energy-st-oringdevice, such as a capacitor 2!.

Suitable control grids 25 maybe introduced into the rectifier chamber inorder to control the initiation of the rectifying arc. The grids may beplaced in one or both of the series-connected devices. If in bothdevices, suitable means should be provided for simultaneously releasingboth grids.

In the modification shown in Fig. 2, both grids are controlled from asingle control source 30, the grids being separated by a high resistance3! of the order of 29,000 ohms, so that in case a backfire shoulddevelop to the grid 25 in one of the chambers 5, the resistance 3! willprevent the loss of control by the grid 25 in the remaining chamber.

In the modification shown in Fig. 3, separate grid control sources, suchas transformers 35, are used. Preferably, both transformers are excitedfrom the single primary feed from a suitable frequency in order toinsure simultaneous operation of both grids.

In the modification according to Fig. 4, each of the grids 25 isprovided with a separate source of excitation current. Preferably, thetransformers 36 are supplied in parallel to insure simultaneousoperation.

In the modification according to Fig. 3, a commutating condenser hasbeen introduced across the supply transformer so that the rectifier maybe operated inverted to supply an alternating-current line with energyfrom a direct-current line. Obviously, this condenser 40 could beeliminated if it was desired to operate the device only to transferenergy from the alternatingcurrent to the direct-current side. Whenoperating as an inverter, the output frequency of the rectifier systemcan be controlled by supplying energy of the desired frequency to thecontrolled grid 25. When operating from the alternatingcurrent to thedirect-current side, the directcurrent voltage maybe controlled byvarying the phase relation of the grid voltage and thealternating-current supply voltage.

In the modification according to Fig. 5, a simple rectifier 5 has beenconnected in series with the usual multi-anode rectifier 60. Preferably,a suitable pumping connection 6! is provided between the simplerectifier and the multianode chamber 69, so that no auxiliary pumpingequipment is needed for the simple rectifier. Since the simple rectifier5 will carry only directcurrent, the arc drop is very low and adds butlittle to the losses of the rectifier as a whole. Since the simplerectifier 5 carries only direct current, no backfires can originatetherein, However, the multi-anode chamber will be subject to backfiresas before the attachment of our invention. However, in case a backfireshould occur in the multi-anode rectifier, the series rectifier willprevent current flowing from the directcurrent circuit and preventdamage on the circuit as Well as materially reduce the damage that mightresult to the rectifier.

Also in case there are other rectifiers feeding the direct-current line,they will not be involved in any way in the backfire in the multi-anoderectifier. Since the backfire in the multi-anode rectifier is limited tothe short circuit current of its own transformer, little damage will beexperienced. Also a considerable saving in the rectifier equipment willresult as the high-speed direct-current circuit breaker is unnecessaryin the operation of rectifiers provided with our invention.

While we have shown and described specific embodiments of our invention,it is apparent that changes and modifications can be made thereinwithout departing from the spirit and scope of our invention. We desire,therefore, that only such limitations shall be imposed as arenecessitated by the prior art or as may be embodied in the accompanyingclaims.

We claim as, our invention:

1. A system for converting direct current to alternating currentcomprising a direct current circuit, an alternating current circuit, aninductance coupling said circuits, a plurality of rectifier means forcontrolling current fiow through said inductance, each rectifier meanscomprising a plurality of series-connected discharge devices, means forcontrolling the initiation of current-carrying arcs in theseries-connected devices, means for extinguishing the current-carryingarc, and energy-storing devices in parallel with each of said dischargedevices.

2. A vapor electric system comprising an alternating current 0' cult, adirect current circuit, a rectifying device for ransferring energybetween said circuits, said device comprising a plurality ofseries-connected discharge chambers, a vaporizable cathode in each ofsaid chambers, an anode closely spaced in respect to said cathode ineach of said chambers, the cathode in one of said chambers beingdirectly connected to the anode of the other, and means in each of saidchambers for controlling the initiation of a current-carrying arctherein.

3. An element for a vapor-electric device having a high servicereliability comprising a unitary discharge structure, a plate fordividing said structure into a plurality of discharge chambers, an anodeand a vaporizing cathode in. each of said chambers, said dividing plateforming the bottom of one chamber and the anode of the other.

LEON R. LUDWIG. JOSEPH SLEPIAN.

